It wouldn't surprise me that the karts you speak of used Kawi engines. I know the single seat planes used Kawi engines at one time. I have sold 440 liquid and fan engine parts to guys running planes also. I just sold a NOS 440 Fan cylinder to a guy in Puerto Rico for use in his plane!
The F-440 Race Cars for SCCA Racing popular in the 90's utilized Kawi 440 liquid engines. They used Aaen twin pipes and Polaris clutches. Racing these would be fun, but I agree... not many places around here to drive them! I would think there would be liability issues even on a track. I would think you would have to belong to a club in order to be "covered" under an insurance "umbrella". As far as the Kawi engines, I believe the Kawi engines became obsolete in karts when the 440 Rotax power plants started showing up. You could extract 80 + hp out of the Bombardier without much sweat. Here is a shot of a race car in 96' running the 440 liquid Kawi engine. Enjoy!